This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-082767, filed Mar. 26, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a camera and a signal processing method thereof. More particularly, the present invention relates to a camera for canceling a dark signal component resulted from an image pick-up device such as a CCD (Charge Coupled Device), and relates to a signal processing method of the camera.
In recent years, mobile tools such as electronic still cameras and notebook personal computers have become widespread as the development of the semiconductor technology has surged forward. Especially, the electronic still camera picks up an image of a subject incident through an objective lens to generate electric signals by using an image sensor, and based on the electric signals displays the image on a liquid crystal display, or stores the image data in a nonvolatile semiconductor memory card. Further, the image data can be captured into a personal computer and subjected to an image processing. Therefore, the electronic still cameras have become widespread rapidly.
Meanwhile, it is known that the CCD which is mounted in the above-described electronic still camera has so-called dark output (dark voltage) characteristics in which output voltage is generated even when incident light is intercepted, and with this dark output, a very small current called dark current is generated.
This dark voltage in the CCD has temperature dependence in which dark voltage is approximately doubled if environmental temperature is varied (increased) about 8xc2x0 C. The dark voltage has the exposure time (electric charge accumulation period) dependence indicative of tendency that the dark voltage is increased as the exposure time is longer under the same temperature condition.
The dark voltage of the CCD becomes noise component and as a result, this is the factor that affects the image data and deteriorates image quality.
As one of techniques for solving this problem, there is a known technique in which image data (dark output component) generated when a mechanical shutter is closed is subtracted from image data (subject image data including dark output component) generated when the mechanical shutter is opened, thereby canceling the noise component from the image data.
However, according to this technique, there is a problem that if the subtraction is carried out using image data which have been subjected to gamma-correction processing having nonlinear characteristics or saturated image data, or if the subtraction is carried out even when the level of the dark output component is low, excellent image data can not be obtained.
Accordingly, it is an object of the present invention to provide a camera capable of carrying out a correcting processing for canceling noise component from image data without deteriorating image quality so as to obtain excellent image data.
According to the present invention, there is provided a camera comprises image pick-up means (an image sensor) for outputting image data in accordance with incident light, first pick-up control means for obtaining first image data output from the image pick-up means under a condition where an incident light path of the image pick-up means is opened, second pick-up control means for obtaining second image data output from the image pick-up means under a condition where the incident light path of the image pick-up means is closed, means for correcting the first image data obtained by the first pick-up control means based on the second image data obtained by the second pick-up control means, nonlinear processing means (a gamma correcting circuit) for subjecting the image data output from the image pick-up means to nonlinear processing, and means for prohibiting the nonlinear processing for the image data by the nonlinear processing means when the first and second image data are obtained by the first and second pick-up control means.
With this structure, the first and second pick-up control means can obtain the first and second image data which are not subjected to the nonlinear processing by the nonlinear processing means. With this feature, it is possible to provide a camera capable of carrying out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and capable of obtaining excellent image data.
According to the present invention, there is provided another camera comprises image pick-up means (an image sensor) for outputting image data in accordance with incident light, first pick-up control means for obtaining first image data output from the image pick-up means under a condition where an incident light path of the image pick-up means is opened, second pick-up control means for obtaining second image data output from the image pick-up means under a condition where the incident light path of the image pick-up means is closed, means for determining whether an isolation point is included in the second image data obtained by the second pick-up control means, and means for correcting the first image data obtained by the first pick-up control means based on a result of the determination made by the determining means.
With this feature, it is possible to provide a camera capable of carrying out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and capable of obtaining excellent image data.
According to the present invention, there is provided a further camera comprises image pick-up means (an image sensor) for outputting image data in accordance with incident light, first pick-up control means for obtaining first image data output from the image pick-up means under a condition where an incident light path of the image pick-up means is opened, second pick-up control means for obtaining second image data output from the image pick-up means under a condition where the incident light path of the image pick-up means is closed, means for determining whether a level of the first image data obtained by the first pick-up control means is saturated, and means for correcting the first image data obtained by the first pick-up control means based on a result of determination made by the determining means and based on the second image data obtained by the second pick-up control means.
With this feature, it is possible to provide a camera capable of carrying out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and capable of obtaining excellent image data.
According to the present invention, there is provided a still another camera comprising image pick-up means (an image sensor) for outputting image data in accordance with incident light, first pick-up control means for obtaining first image data output from the image pick-up means under a condition where an incident light path of the image pick-up means is opened, second pick-up control means for obtaining second image data output from the image pick-up means under a condition where the incident light path of the image pick-up means is closed, means for detecting a temperature around the image pick-up means, and means for correcting the first image data obtained by the first pick-up control means based on the temperature detected by the temperature detecting means and based on the second image data obtained by the second pick-up control means.
With this feature, it is possible to provide a camera capable of carrying out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and capable of obtaining excellent image data.
According to the present invention, there is provided a still further camera comprises image pick-up means (an image sensor) for accumulating electric charges corresponding to incident light, converting accumulated electric charges into image data, and outputting the image data, first pick-up control means for obtaining first image data output from the image pick-up means under a condition where an incident light path of the image pick-up means is opened, second pick-up control means for obtaining second image data output from the image pick-up means under a condition where the incident light path of the image pick-up means is closed, means for detecting an electric charge accumulation period of the image pick-up means, and means for correcting the first image data obtained by the first pick-up control means based on the electric charge accumulation period detected by the detecting means and based on the second image data obtained by the second pick-up control means.
With this feature, it is possible to provide a camera capable of carrying out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and capable of obtaining excellent image data.
According to the present invention, there is provided a signal processing method for a camera which carries out nonlinear processing for image data output from an image sensor, comprises a step of prohibiting the nonlinear processing for the image data output from the image sensor under a condition where an incident light path of the image sensor is opened, thereby obtaining first image data which are not subjected to the nonlinear processing, a step of prohibiting the nonlinear processing for the image data output from the image sensor under a condition where the incident light path of the image sensor is closed, thereby obtaining second image data which are not subjected to the nonlinear processing, and a step of correcting the first image data based on the second image data.
With this feature, it is possible to carry out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and to obtain excellent image data.
According to the present invention, there is provided another signal processing method for a camera, comprises a step of obtaining first image data output from an image sensor under a condition where an incident light path of the image sensor is opened, a step of obtaining second image data output from an image sensor under a condition where an incident light path of the image sensor is closed, a step of determining whether an isolation point is included in the second image data, and a step of correcting the first image data based on a result of the determination.
With this feature, it is possible to carry out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and to obtain excellent image data.
According to the present invention, there is provided a further signal processing method for a camera, comprises a step of obtaining first image data output from an image sensor under a condition where an incident light path of the image sensor is opened, a step of obtaining second image data output from an image sensor under a condition where an incident light path of the image sensor is closed, a step of determining whether a level of the first image data is saturated, and a step of correcting the first image data based on a result of the determination and the second image data.
With this feature, it is possible to carry out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and to obtain excellent image data.
According to the present invention, there is provided a still another signal processing method for a camera, comprises a step of obtaining first image data output from an image sensor under a condition where an incident light path of the image sensor is opened, a step of obtaining second image data output from an image sensor under a condition where an incident light path of the image sensor is closed, a step of detecting a temperature around the image sensor, and a step of correcting the first image data based on the second image data when the detected temperature satisfies a predetermined condition.
With this feature, it is possible to carry out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and to obtain excellent image data.
According to the present invention, there is provided a still further signal processing method for a camera, comprises a step of obtaining first image data output from an image sensor under a condition where an incident light path of the image sensor is opened, a step of obtaining second image data output from an image sensor under a condition where an incident light path of the image sensor is closed, a step of detecting an electric charge accumulation period of the image sensor, and a step of correcting the first image data based on the second image data when the detected electric charge accumulation period satisfies a predetermined condition.
With this feature, it is possible to carry out the correction processing for canceling the noise component from the image data without deteriorating the image quality, and to obtain excellent image data.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.
The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.